The present invention is related to copending U.S. Pat. application, Ser. No. 668,527, filed on Mar. 19, 1976, now U.S. Pat. No. 4,117,884, issued Oct. 3, 1978, which is directed to a process for the production of a tubular heat exchanger wherein a tube bundle consisting of tubes made of silica glass is cast into a casting resin at the tube ends thereof, the vertically arranged tube bundle being inserted with the tube ends being disposed in troughs provided with holes in the bottom thereof for receiving the tube ends. The troughs are subsequently filled with a casting resin whereupon the liquid casting enters, due to a capillary effect, the annular gaps between the holes and the tube ends. The disclosure of this United States Patent and/or of the parallel German Application DOS No. 2,610,817, is fully incorporated into the present invention by reference.
This process, on the whole, has proven itself well, especially on account of the fact that an annular gap is formed between the holes of the trough and the tubes, e.g., silica glass tubes, forming the tube bundle. This gap is filled in a subsequent process step with the casting resin by capillary action. Thus, the material of the tubes is nowhere in contact with the material of the trough. Rather, the casting resin forms a continuous barrier between these two elements. Advantageously, the casting resin is a silicone resin. Because of this procedure, the thermal stresses, which occur during operation and are frequently considerable, are compensated for and absorbed.
The present invention is based on the problem of further developing the process according to my U.S. Pat. No. 4,117,884 so that even the aforementioned thermal stresses between the mounted tube bundles and the metallic housing surrounding the tube bundle or bundles are substantially avoided. To solve this problem, according to the present invention, the troughs with the tube bundle are inserted in a metallic housing so that a gap is formed between the sidewalls of the troughs and the metallic housing, said gap being subsequently filled with the casting resin. Because of this measure, the thermal stresses existing between the metallic housing and the troughs holding the tube bundles are absorbed, since the casting resin is disposed between these two components, which are likewise subject to strong thermal expansions.
Any casting resin which, after vulcanizing, assumes within a few hours the Shore hardness which approximates that of an eraser, can be used in the present invention. The preferred resin is a silicone resin, e.g., organosiloxane polymers. The troughs remaining in the heat exchanger and consisting of sheet metal thus serve as a kind of lost form.
Another preferred feature of the present invention is that the tubes of the tube bundle are placed on a spacer board prior to the casting of the casting resin. The spacer board equalizes any existing differences in the vertical level among the tubes.
A heat exchanger produced according to the present invention is characterized in that the lowermost trough rests on a horizontal flange on the inside of the metallic housing. This provides the necessary support for the tube bundles by the metallic housing, preferably a steel housing.
Several such tube bundles can be produced in separate troughs in the above-described manner to produce modules. In this case, it is preferred to utilize several such modules in the metallic housing.